JP2001159582A - Method for inspecting composite polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection method capable of effectively and simply inspecting for flows existing on a surface of a phase difference plate formed with a nonreflective layer constituting a composite polarizing plate. SOLUTION: In this method for inspecting the composite polarizing plate 13, light from a light source 3 is projected on a phase difference plate 13 side of the composite polarizing plate 10 comprised by laminating the phase difference plate 13 and a linear polarizing plate 12 for observing the reflected light through an analyzer 5. The analyzer 5 is constituted by laminating an analyzer linear polarizing plate 9 and an analyzer phase difference plate 7 with an inplane retardation the same as an inplane retardation of the phase difference plate 13 of the composite polarizing plate 10, and the analyzer phase difference plate 7 side is arranged on the composite polarizing plate 10 side. The linear polarizing plate 12 of the composite polarizing plate and the analyzer linear polarizing plate 9 are provided as a crossed nicol, and a delay axis of the phase difference plate 13 of the composite polarizing plate 10 and a delay axis of the analyzer phase difference plate 7 are mutually perpendicularly crossed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a composite polarizing plate in which a retardation plate and a linear polarizing plate are laminated, and more particularly, to an inspection of a composite polarizing plate used between a liquid crystal cell and an air layer. More particularly, the present invention relates to a method for inspecting defects such as bubbles, scratches, foreign matter, pinholes, and unevenness present on the surface of or inside a retardation plate.

[0002]

2. Description of the Related Art A composite polarizing plate in which a retardation plate and a linear polarizing plate are laminated is usually attached to the surface of a liquid crystal cell in such a manner that the retardation plate contacts the surface of the liquid crystal cell. Used as part of the display panel.

In recent years, projectors for directly projecting a liquid crystal display image on a screen have been increasingly used. In such a liquid crystal display projector,
A strong light source is used to ensure the brightness of the projected image.

A linear polarizer used in a composite polarizer absorbs about 50% of incident light and transmits light parallel to a transmission axis, and the absorbed light is converted into heat. Many conventional liquid crystal displays use a battery as a power source, and use a light source whose power consumption is reduced as much as possible. Heat generated in a linear polarizing plate is not a problem.

However, when a powerful light source such as a projector is used, such heat generation is large, and the temperature of a liquid crystal cell or the like in a composite polarizing plate or a liquid crystal display in which such a polarizing plate is laminated increases, which adversely affects its characteristics. May give. In order to avoid the influence of such a rise in temperature, the liquid crystal display projector employs a configuration in which a space is provided between the liquid crystal cell and the composite polarizing plate with the phase difference plate surface facing the liquid crystal cell.

If a space is provided between the liquid crystal cell and the composite polarizing plate, 4 to 5% of the light constituting the image passing through the liquid crystal cell is reflected on the surface of the phase difference plate, causing bleeding and the like, and the image becomes less sharp. descend. In order to prevent the reflection of light, a non-reflection layer may be formed by applying a non-reflection coating to the surface of the phase difference plate.

The anti-reflection layer formed on the surface has a reflectivity on the surface of the retardation plate of usually 1% or less, preferably 0.5% or less. Therefore, since the reflected light is weak, the transmitted light transmitted from the opposite surface, and the reflected light from the inspection light source that passes through the phase difference plate and the linear polarizer to reach the opposite surface and is reflected there ( (Hereinafter, referred to as interference light), it is difficult to detect a defect such as a foreign substance or a portion where the anti-reflection coating layer is missing. In particular, defects having a diameter of about 20 to 30 μm, and linear scratches having a width of about 2 to 3 μm or less even when the length was about 20 to 30 μm were hardly detected.

As a method of blocking the above interfering light, a linear polarizing plate, which is a component of a composite polarizing plate to be inspected, is used, and a linear polarizing plate having a cross Nicol relationship with the linear polarizing plate is used as an analyzer. Means provided in the inspection unit and observed through this linear polarizing plate can be considered. In other words, the interfering light is linearly polarized light because it passes through the linear polarizing plate, which is a component of the composite polarizing plate, and the linearly polarized light is absorbed by the linear polarizing plate having an absorption axis orthogonal to the absorption axis. It is intended to eliminate the interfering light by utilizing the characteristic of being disturbed.

However, the interfering light, which has been converted into linearly polarized light by the linear polarizing plate, which is a component of the composite polarizing plate, becomes elliptically polarized light when passing through the phase difference plate, and passes through the linear polarizing plate, which is the analyzer. This causes a phenomenon called “light transmission” to obstruct observation of surface reflected light.

[0010]

SUMMARY OF THE INVENTION The present invention effectively and simply eliminates defects existing on the surface of a retardation plate of a composite polarizing plate, particularly a composite polarizing plate having a non-reflection layer formed on the surface of the retardation plate. An inspection method for inspection is provided.

[0011]

SUMMARY OF THE INVENTION According to the present invention, there is provided a composite polarizing plate comprising a laminate of a retardation plate and a linear polarizing plate, which is illuminated with light to the retardation plate side, and the reflected light is observed through an analyzer. A method for inspecting a composite polarizing plate, wherein the analyzer is formed by laminating an analyzer retardation plate and an analyzer linear polarizing plate having an in-plane retardation equal to the in-plane retardation of the retardation plate of the composite polarizing plate. An analyzer arranged so that the analyzer phase difference plate side is positioned on the composite polarizing plate side, wherein the linear polarizing plate of the composite polarizing plate and the analyzer linear polarizing plate are crossed with each other. And the slow axis of the phase difference plate of the composite polarizing plate and the slow axis of the analyzer phase difference plate are orthogonal to each other.

Here, the in-plane retardation is a numerical value defined below.

[0013] plane retardation _{= (n x -n y) ·} d n x: refractive index in the x-axis direction of the phase difference plate (slow axis direction) n _y: y-axis direction of the retardation film (slow axis D): the thickness of the retardation plate When the linear polarizers are cross-Nicol, transmitted light is blocked as is well known. However, when a retardation plate is laminated on a linear polarizing plate and observed using an analyzer including only the linear polarizing plate, light leakage occurs as described above.

In the present invention, the surface of the retardation plate of the composite polarizing plate to be inspected is irradiated with light from a light source, and the reflected light is first observed through an analyzer retardation plate and then through an analyzer linear polarizing plate. The interfering light passes through the linear polarizer of the composite polarizer to become linearly polarized light, and then passes through the retarder and the analyzer retarder of the composite polarizer. Since the in-plane retardations are equal to each other and their slow axes are orthogonal to each other, the effects of these retardation plates are eliminated. Therefore, the crossed Nicols effect of the two linear polarizing plates is exerted, the transmitted light is absorbed, and the reflected light on the surface of the retardation plate of the composite polarizing plate can be clearly observed.

In the above invention, the composite polarizing plate and the analyzer are arranged in parallel, and the sum of the Nz coefficient of the phase difference plate of the composite polarizing plate and the Nz coefficient of the phase difference plate of the analyzer is provided. Is preferably set to 1. Here, the Nz coefficient is a numerical value defined below.

The Nz coefficient _{= (n x -n z) /} (n x -n y) n x: refractive index in the x-axis direction of the phase difference plate (slow axis direction) n _y: y-axis direction of the retardation plate Refractive index in the direction (perpendicular to the slow axis) _nz : Refractive index in the z-axis direction (thickness direction) of the retardation plate Light for surface inspection is usually applied obliquely to the composite polarizing plate. You. Accordingly, interfering light such as transmitted light that obstructs surface observation is also light in the same oblique direction. Since the refractive index of the phase difference plate is different in the x-axis direction, the y-axis direction, and the z-axis direction, that is, the slow axis of the phase difference plate, the direction orthogonal to the slow axis, and the thickness direction, the light in the oblique direction is different. Causes a phase difference (retardation) corresponding to the refractive index of the retardation plate in the oblique direction and the length of the transmitted light path. Therefore, simply making the in-plane retardation of the retardation plate of the composite polarizing plate and the in-plane retardation of the analyzer retardation plate the same does not completely eliminate the effects of both retardation plates, and causes a slight shift. Light leakage may occur by that much.

When the sum of the Nz coefficients is set to 1 as described above,
Light leakage of obliquely transmitted interference light is more completely prevented, and surface inspection is facilitated. If the intensity of the interfering light is weaker than the reflected light and the degree of the interfering light is low and a defect can be detected, the sum of the Nz coefficients need not be exactly 1 but may be approximately 1.

The present invention is particularly suitable as a method for inspecting a composite polarizing plate having a non-reflection layer at least on the outer surface of the retardation film.

As a result of the absorption of the interfering light, a non-reflective layer is provided, and the surface inspection of the retardation plate of the composite polarizing plate with weak reflected light can be performed more reliably.

[0020]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a method for inspecting a composite polarizing plate. The composite polarizing plate 10 to be inspected has a linear polarizing plate 12 and a phase difference plate 13 laminated and integrated. In the inspection section D, an analyzer 5 is provided, and light arriving from the composite polarizing plate is observed through the analyzer 5. In a composite polarizing plate used for a projector or the like, a retardation plate 1
An anti-reflection layer is provided on the surface opposite to the surface on which the linear polarizing plate is laminated.

The analyzer 5 is a phase difference plate (analyzer phase difference plate).
7 and a linear polarizer (analyzer linear polarizer) 9 are laminated, and the analyzer phase difference plate 7 is disposed parallel to and opposed to the phase difference plate 13 of the composite polarizing plate 10 to be inspected. ing.
The analyzer phase difference plate 7 and the phase difference plate 13 have the slow axes orthogonal to each other and the same in-plane retardation. Preferably, the Nz coefficient of the analyzer phase difference plate 7 and the Nz coefficient of the phase difference plate 13 are preferable. Is approximately 1.

The linear polarizer 9 of the analyzer 5 and the linear polarizer 12 of the composite polarizer 10 to be inspected are arranged so as to be in a crossed Nicols state. The interfering lights b and c are both linearly polarized light because they pass through the linearly polarizing plate 12, and can be absorbed by the linearly polarizing plate 9 of the analyzer 5 if the effect of the retardation plate is eliminated. Becomes

A part of the light emitted from the light source 3 is reflected on the surface of the phase difference plate and reaches the inspection section D as a. Some other light passes through the composite polarizer 10 and reaches the opposite surface,
The light is reflected here and further passes through the phase difference plate to reach the analyzer 5 (b).

Light incident from the opposite side of the composite polarizing plate from the light source passes through the composite polarizing plate and reaches the analyzer 5 (c).

The light beams b and c are interfering light beams that obstruct the visual recognition of the light beam a necessary for inspecting the surface of the phase difference plate 13. And is absorbed by the analyzer linear polarizer 9 as a result,
Interference is eliminated.

Known linear polarizing plates and retardation plates used in the present invention can be used without limitation.

As the retardation plate, those having different Nz coefficients are commercially available, and are appropriately selected and used according to the inspection object.
For example, for inspection of a composite polarizer using a retardation plate having an Nz coefficient of 0.5, a retardation plate having an Nz coefficient of 0.5 is used as an analyzer retardation plate, and an Nz coefficient of about 0.3 is used. Inspection of a composite polarizing plate using a retardation plate uses a retardation plate with an Nz coefficient of 0.7 as an analyzer retardation plate and an inspection of a composite polarizing plate using a retardation plate with an Nz coefficient of 0.7. , A phase difference plate having an Nz coefficient of 0.3 is used as an analyzer phase difference plate.

The analyzer linear polarizing plate 9 may be made of another material having a linear polarizing action. As a result of the inspection, if a defect is found, if the defect is not yet punched into a predetermined shape, the portion may be marked and removed from the punched portion, and if the product has been punched, the product may be discarded.

In the above, an example in which the inspection is performed visually has been described, but the obtained image may be processed by a computer using an optical device such as a camera.

The composite polarizing plate may be an elliptically polarizing plate, or may have an in-plane retardation of 1 / 4λ (130 to 140).
(about nm) may be a circularly polarizing plate laminated such that the slow axis and the absorption axis cross each other at 45 °.

[Brief description of the drawings]

FIG. 1 is a model diagram showing an example of a method for inspecting a phase difference plate surface of a composite polarizing plate.

[Explanation of symbols]

 Reference Signs List 3 light source 5 analyzer 7 analyzer retarder 9 analyzer linear polarizer 10 composite polarizer 12 linear polarizer 13 retarder D inspection unit a reflected light b, c interference light

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA49 BB01 BB17 CC21 DD00 DD12 FF42 FF49 GG02 JJ03 JJ12 LL33 LL34 LL35 2G086 EE10 2H049 BA02 BA06 BB03 BC01 2H091 FA08X FA08Z FA11X FA11LA FC12 LA

Claims (3)

[Claims] 1. A method for inspecting a composite polarizing plate, comprising: irradiating light on the retardation plate side of a composite polarizing plate having a retardation plate and a linear polarizing plate laminated, and observing reflected light thereof through an analyzer. The analyzer comprises a laminate of an analyzer retardation plate and an analyzer linear polarizer having an in-plane retardation equal to the in-plane retardation of the retardation plate of the composite polarizing plate. An analyzer arranged so that a retardation plate side is positioned on the composite polarizing plate side, wherein the linear polarizing plate of the composite polarizing plate and the analyzer linear polarizing plate are crossed Nicols, and the composite polarizing plate is Wherein the slow axis of the retardation plate and the slow axis of the analyzer retardation plate are orthogonal to each other. 2. The composite polarizing plate and the analyzer are disposed in parallel with each other, and the sum of the Nz coefficient of the phase difference plate of the composite polarizing plate and the Nz coefficient of the analyzer phase difference plate is set to 1. Item 7. An inspection method of the composite polarizing plate according to Item 1. Nz factor _{= (n x -n z) /} (n x -n y) n x: refractive index in the x-axis direction of the retardation plate n _y: refractive index in the y-axis direction of the retardation film n _z: retarder In the z-axis direction 3. The method for inspecting a composite polarizing plate according to claim 1, wherein the composite polarizing plate has a non-reflection layer at least on an outer surface of a retardation film.